/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.io;

import java.io.IOException;
import java.io.Reader;
import java.util.Iterator;

import com.google.common.base.Preconditions;

/**
 * A {@link Reader} that will concatenates multiple readers
 * 
 * @author Bin Zhu
 * @since 2009.09.15 <b>tentative</b>
 */
class MultiReader extends Reader {
    private final Iterator<? extends InputSupplier<? extends Reader>> it;
    private Reader current;

    MultiReader(Iterator<? extends InputSupplier<? extends Reader>> readers)
            throws IOException {
        this.it = readers;
        advance();
    }

    /**
     * Closes the current reader and opens the next one, if any.
     */
    private void advance() throws IOException {
        close();
        if (it.hasNext()) {
            current = it.next().getInput();
        }
    }

    @Override
    public int read(char cbuf[], int off, int len) throws IOException {
        if (current == null) {
            return -1;
        }
        int result = current.read(cbuf, off, len);
        if (result == -1) {
            advance();
            return read(cbuf, off, len);
        }
        return result;
    }

    @Override
    public long skip(long n) throws IOException {
        Preconditions.checkArgument(n >= 0, "n is negative");
        if (n > 0) {
            while (current != null) {
                long result = current.skip(n);
                if (result > 0) {
                    return result;
                }
                advance();
            }
        }
        return 0;
    }

    @Override
    public boolean ready() throws IOException {
        return (current != null) && current.ready();
    }

    @Override
    public void close() throws IOException {
        if (current != null) {
            try {
                current.close();
            } finally {
                current = null;
            }
        }
    }
}
